This may not pertain to all 3x AAA flashlights, but with some calipers and common sense, you can probably check for yourself.
Step 1: The Background
I bought a cheap UV flashlight the other day to augment my pet detective toolset.
The initial problem was this: the flashlight is supposed to take 3xAAA batteries. Harummph, I say. Completely useless. I bought it anyway, figuring I'd modify it to take a useful battery type.